The objective of the research is to elucidate the participation of certain metabolically significant chemicals in the mechanisms which mediate local regulation of blood flow. The literature suggests that the most likely chemical candidates for such a role are 02, K ions, H ions and adenosine or its mononucleotides. During the current year we have shown that adenosine and/or AMP appear in coronary sinus blood during local cardiac hypoxia and on relief of temporary ischemia. It is hoped that during the next year we can distinguish which of these agents appear in coronary sinus blood during the above responses or if, in fact, both increase. This will be attempted by administration of an enzyme (adenosine deaminase) that degrades adenosine but not AMP. Also, in the artifically perfused guinea pig heart we will chemically determine the levels of AMP in the sinus effluent before, during and following local cardiac hypoxia and ischemia. BIBLIOGRAPHIC REFERENES: Stowe, D.F., T.L. Owen, D.K. Anderson, F.J. Haddy and J.B. Scott: Interaction of 02 and C02 in sustained exercise hyperemia of canine skeletal muscle. Amer. J. Physiol. 229: 28-33, 1975. Owen, T. Lon, Ina C. Ehrhart, W. Jeffrey Weidner, Jerry B. Scott and Francis J. Haddy: Effects of indomethacin on local blood flow regulation in canine heart and kidney. Proceed. Soc. Exp. Bio. and Med. 149:871-876, 1975.